This invention relates to heat-sealable polyolefin elastomer vulcanizates.
Articles of vulcanized polyolefin elastomers are primarily utilized, as is known, in applications where high requirements must be met with respect to resistance against the effects of weathering and aging. Thus, a desirable application in the building industry is, for example, the utilization of sheets of ethylene-propylene copolymers (EPM), ethylenepropylene-diene terpolymers (EPDM) or butyl rubber (BR) as roof covering. In this type of roofing, tightness is largely determined and limited by the rather problematical way of laying the sheets to form seams or overlapping portions. For this reason, several attempts have already been made to join articles of vulcanized polyolefin elastomers with each other or with articles of other materials.
Thus, it has been known from DAS (German Published Application) No. 1,620,832 to conduct a process for the manufacture of a solid adhesive bond between polyethylene and natural or synthetic rubber by vulcanization with the use of heat and pressure, characterized in that polyethylene having a melt index of less than 0.15 is used. The polyethylene is preferably applied in powder form to the surface of the rubber before the exertion of pressure and exposure to heat. However, the polyethylene can also be applied in the form of a film.
It is known from DOS (German Unexamined Laid-Open Application) No. 2,004,379 to establish adhesive bonds between vulcanized layers of elastomeric copolymers and/or terpolymers of ethylene with an .alpha.-olefin and a selective polyene and/or butyl rubber, if there is inserted between these elastomeric layers a plastomeric layer of a thermoplastic polymer and/or copolymer of ethylene, propylene and/or butene which is free of substituent groups having a polar character and free of reactive groups, and the thus-combined layers are subjected to the effect of heat, preferably under pressure.
Finally, a process is known from DOS No. 2,322,594 for bonding a molded article of an ethylene/propylene copolymer rubber (EPM) or an ethylene/propylene/diolefin copolymer rubber (EPDM) with a polyolefin resin.
All of the processes and/or measures of the above-discussed state of the art, however, exhibit more or less serious practical deficiencies. For example, it is only possible by means of the process according to DOS No. 2,322,594 to join molded articles of an ethylene/propylene or ethylene/propylene/diene copolymer with an article of a thermoplastic material (synthetic polyolefin resin), but it is impossible thereby to connect molded articles of EPM or EPDM with each other.
The use of pulverulent polyolefin hot-melt adhesives according to DOS No. 1,620,832 has the disadvantage, above all during the sealing of rubber roofing sheets, that the powder frequently does not remain at the point provided for the heat-sealing step due to the inclination of the roof, wind and the heat-sealing device used for the welding step. The use of very thin film strips according to DOS's Nos. 1,620,832 and 2,004,379 is often made difficult for the same reason.
When using film strips of a polyolefin, four surfaces must be heated almost uniformly and must be held in the correct position. A previously conducted strip-shaped coating of the roofing sheets to be glued together at the zones intended for the welding step is possible, but unsatisfactory since additional welds are necessary in view of the deviations from the laying pattern (chimneys, eaves, etc.) unavoidable under practical conditions. When using polyolefin film strips, there is the additional danger that individual droplets are formed during the complete melting of the polyolefin, leading to a non-uniform and thus leaking weld.